The 1947 - Present Chevrolet & GMC Truck Message Board Network - View Single Post

roboticjunky · 10-23-2018, 06:34 PM

If you can found a good scanner that tells you what your sensors are reading, that will really help.

I had a truck that had TBI and ran rich and would die when you put in gear. MAP sensor wasn't reading right. Ended being the wire going from the MAP sensor to the ECM was bad. So that bad wire made the ECM think it at full throttle and ran really rich. Bad o2 sensor could also make it run rich. Bad coolant sensor would also make the motor run rich, because the ECM will think it's really cold when it's not.

You can check the MAP sensor by using a multimeter and checking to see if it's getting 5 volts from the ECM. Then you can check how much voltage is going back to the ECM should be around 4.90 volts or so. You can also check your coolant sensor, which is next to the thermostat housing, by unplugging the coolant sensor and setting your multimeter to ohms. Then check the resistance across the 2 prongs on the coolant sensor. Reading should be around 5670 if the motor temperature is 50 degrees F.

Also do a visible check like is everything plugged into the sensors and are there any broken or burnt wires.

10-23-2018, 06:34 PM	#8
roboticjunky Registered User Join Date: Oct 2015 Location: IN Posts: 208	Re: Question about tbi to Rochester 2 barrel If you can found a good scanner that tells you what your sensors are reading, that will really help. I had a truck that had TBI and ran rich and would die when you put in gear. MAP sensor wasn't reading right. Ended being the wire going from the MAP sensor to the ECM was bad. So that bad wire made the ECM think it at full throttle and ran really rich. Bad o2 sensor could also make it run rich. Bad coolant sensor would also make the motor run rich, because the ECM will think it's really cold when it's not. You can check the MAP sensor by using a multimeter and checking to see if it's getting 5 volts from the ECM. Then you can check how much voltage is going back to the ECM should be around 4.90 volts or so. You can also check your coolant sensor, which is next to the thermostat housing, by unplugging the coolant sensor and setting your multimeter to ohms. Then check the resistance across the 2 prongs on the coolant sensor. Reading should be around 5670 if the motor temperature is 50 degrees F. Also do a visible check like is everything plugged into the sensors and are there any broken or burnt wires.